It is often desirable to provide electric power to an area that is separated from the main powered areas by a wall or window. The wall or window makes the use of an extension cord less practical to provide this power. For example, an extension cord might require that a window or door be left open to allow the cord to pass therethrough.
For example, it may be convenient to use a laptop PC on the balcony or terrace where there is no electrical socket. It may be useful to put sensors on the outside of a house, for example to power a burglar alarm or television monitor. It may be desirable to bring a television outdoors.
One way to do this is to wire the new area; to drill a hole through a wall for example. However, this may not be allowed, for example in a rental apartment or condo. It may be cost prohibitive and/or inconvenient. Or, the user simply might not want to do it.